1. Field of the Invention
The present invention relates to a printer that performs printing on a recording medium, such as a recording sheet, according to image information.
2. Description of the Related Art
In general, printers having the simplest configuration include two units, a sheet storage unit that contains recording sheets, and an image forming unit. Examples of configurations of the printers will be described with reference to FIGS. 16 to 18.
FIGS. 16A, 16B, and 16C are a perspective view, a plan view, and a side view, respectively, of a printer in which a sheet storage unit 11 (a dotted area indicates the largest possible recording sheets on which image formation is possible) is horizontally placed, and is connected at one end to an image forming unit 12. Recording sheets are supplied, fed, subjected to image formation, and ejected in the direction of the arrow in FIG. 15C. In this case, the installation area S of the printer is large, but the height H is small. This printer is disclosed in, for example, Japanese Patent Laid-Open No. 2002-68519.
FIGS. 17A, 17B, and 17C are a perspective view, a plan view, and a side view, respectively, of a printer in which a sheet storage unit 21 (a dotted area indicates the largest possible recording sheets on which image formation is possible) is vertically placed, and is connected at one end to an image forming unit 22. Recording sheets are supplied, fed, subjected to image formation, and ejected in the direction of the arrow in FIG. 17C. In this case, the height H is larger, but the installation area S is smaller than in the printer shown in FIG. 16A to 16C. This printer is disclosed in, for example, Japanese Patent Laid-Open No. 7-68771.
FIGS. 18A, 18B, and 18C are a perspective view, a plan view, and a side view, respectively, of a printer in which a sheet storage unit 31 (a dotted area indicates the largest possible recording sheets on which image formation is possible) is horizontally placed, and an image forming unit 32 is provided thereon. Recording sheets are supplied, fed, subjected to image formation, and ejected in the direction of the arrow in FIG. 18C. In this case, the height H is larger than in the printer shown in FIGS. 16A to 16C, and the installation area S is larger than in the printer shown in FIGS. 17A to 17C. However, the height H and the installation area S are well balanced. This printer is disclosed in, for example, Japanese Patent Laid-Open No. 5-32349.
The first common characteristic of the above three printers is that the largest possible recording sheet on which image formation is possible is conveyed in the longitudinal direction thereof through the image forming means for image formation.
Image forming means of current printers adopt various recording methods such as electrophotography, ink-jet printing, and thermal printing. Regardless of the recording method, side plates serving as structures are provided on both sides of a feeding path in the feeding direction of a recording sheet in the image forming means. Since ends of feeding rollers and ends of element components for image formation are supported by the side plates, the lengths of the feeding rollers and the element components can be reduced by shortening the distance between the side plates. It is obvious that a smaller length of the element components improves various mechanical characteristics, for example, machining accuracy and time, material cost, machining cost, positioning accuracy during assembly, flexure strength, and ease of assembly. It is also obvious that the distance between the side plates needs to be longer than the width of the recording sheet that passes therebetween. For this reason, in most printers, a recording sheet is conveyed in the longitudinal direction thereof so that the direction of its short sides coincides with the width direction of the feeding path. A converse configuration in which the recording sheet is conveyed in the direction of its short sides so that the direction of its long sides coincides with the width direction of the feeding path is also practically used because printing on the entire recording sheet is completed in a period shorter than in the above configuration when the recording speed per unit length is not changed. However, it is more advantageous to improve the mechanical characteristics by reducing the lengths of the element components. Therefore, in the great majority of practical printers, the recording sheet is conveyed in the longitudinal direction thereof so that the direction of its short sides coincides with the width direction of the feeding path in the image forming means.
The second common characteristic of the above three printers is that the longer dimension of the image forming means is larger by at least approximately 10 mm than the shorter dimension of the largest possible recording sheet on which image formation is possible. As described above, side plates serving as structures are provided on both sides in the feeding direction of the feeding path of the image forming means in which the recording sheet passes, the distance between the side plates is longer than the width of the largest possible recording sheet, and the side plates support the ends of the feeding rollers and the element components for image formation. Outside the side plates, there are provided components that cannot be placed in a region, through which the recording sheet passes during printing, in terms of design and components that may be placed in the region, but should be placed outside the region if possible. The components that cannot be placed in a region, through which the recording sheet passes during printing, in terms of design are, for example, mechanical components such as gears for driving rollers, and fixed components such as bearings. Since these components must input driving force to the rollers for feeding the recording sheet without interfering with the fed recording sheet, they cannot be placed in the region. The components that may be placed in the region, but should be placed outside the region if possible are, for example, electrical components such as motors, power boards, and control boards. Since these components include large parts such as motor cases and electrolytic capacitors, when they are placed in the region, the height of the printer increases. Therefore, these components should be placed outside the region if possible. Furthermore, since the stability of operation of wires that are easily affected by electrical noise, such as signal lines for a thermal head, increases as the length of the wires decreases, it is usual to place control boards on both sides in order to reduce the lengths of the wires. As described above, reasonable dimensions are necessary outside the side plates. The longer dimension of the image forming means is determined with reference to the upper limit of the outside dimension, for example, the dimension of the motor serving as a rotating source for the rollers, and, in general, is larger by at least approximately 10 mm than the width of the largest possible recording sheet on which image formation is possible.